What is the minimum amount of nitrogen to be removed from the air separation distillation column?

There is no minimum amount that needs to be removed for impure nitrogen; this depends on your requirements for oxygen and nitrogen. In an ideal situation, there is no impure nitrogen present. Oxygen makes up 20.93% of air, while nitrogen accounts for 78.12%; the remaining portion consists of noble gases! ! ! !

Thank you for your reply. I hope to separate as much oxygen and nitrogen as possible from the compressed air, without producing contaminated nitrogen; however, when I discussed this with the manufacturer, they said it’s not possible to avoid producing contaminated nitrogen.

It’s definitely impossible to avoid nitrogen pollution. Your molecular sieve still needs dirty nitrogen for desorption. Generally speaking, the ratio of the minimum amount of contaminating nitrogen to the volume of inlet air can be reduced to around 18%. These gases must be extracted. Moreover, when you reduce the extraction amount to such a low level, it becomes necessary to use a pre-cooling system, such as an ice machine, to lower the inlet temperature of the molecular sieve. Also, for processes that do not involve argon, the argon fraction is actually removed along with the contaminated nitrogen; otherwise, the oxygen-nitrogen product would definitely be substandard

I agree with what was said above; ignoring the process involving argon, the argon fraction is removed from the contaminated nitrogen in order to ensure that the oxygen and nitrogen products meet the required standards.

Our nitrogen purity of 99.9% is sufficient. If molecular sieve regeneration is considered, the purified dry air can be used for this purpose; since the pressure is high, less contaminated nitrogen should be required

Is what was said on the 7th floor a special case? Just nitrogen? Doesn’t it need oxygen? If you use dry air as the regenerating gas, it means that the amount of air entering the cold box decreases, and the oxygen contained in this air cannot be extracted. Given the ratio of oxygen to nitrogen in the air, which is 1:4, it’s not really cost-effective to do it this way. Also: low nitrogen purity can be addressed through various methods. For example, reducing the number of trays in the tower (which helps to save initial investment), or increasing the load on the reboiler to raise the purity at the midpoint, and so on. But in any case, a low purity of nitrogen means a low yield of oxygen. Finally, argon tends to enter oxygen rather than nitrogen. If you don’t discharge nitrogen, the oxygen purity is affected

I believe the amount of nitrogen that can be extracted is closely related to the design of each unit, and the relationship is quite significant. If the design does not allow for an appropriate amount of extraction, or if that amount is increased or decreased beyond the distillation capabilities of the distillation tower, it will definitely affect the purity of the final product. For each air separation unit, there is a certain range for the amount of nitrogen that can be extracted; too much or too little is not good! ! If you need a large volume of pure nitrogen, it is possible to make appropriate adjustments by reducing the amount of contaminated nitrogen taken out and increasing the amount of nitrogen taken out, and vice versa. Oxygen makes up 20.93% of the air, nitrogen accounts for 78.12%, argon constitutes 0.9%, and the remaining rare gases make up 0.04%.

What the original poster means is to extract as much nitrogen and oxygen as possible, and this is achievable – it’s possible to separate them all under ideal conditions. The reason air separation manufacturers say this is that complete separation can be accomplished under ideal conditions, with an unlimited number of distillation stages, but in practice it’s not feasible. Moreover, regenerating molecular sieves requires gas; compressed air can be used for this purpose, but it’s not economical, as molecular sieves are regenerated at atmospheric pressure. Of course, regeneration at operating pressure is also possible, but this would increase the amount of gas needed for regeneration, as reducing pressure itself is a process of desorption, which can help reduce the amount of gas required for regeneration. Using compressed air for regeneration would result in energy waste. Moreover, reality is not an ideal state, and towers cannot be built infinitely tall; therefore, a certain amount of nitrogen oxides will inevitably be produced. Furthermore, the statement about the argon-enriched area upstairs is incorrect; most of the argon is concentrated in the nitrogen area. You can check the books, as it’s explained clearly there. In a situation like yours, you can ask the manufacturer to come up with a plan for you. All you need to do is specify the size of the air separation unit you want to build, as you aim to extract as much oxygen and nitrogen as possible. The manufacturer will then provide you with a reasonable plan in terms of energy consumption and investment costs. Meet your needs.

Dirty nitrogen gas needs to be extracted. The current air separation distillation towers are not capable of achieving optimal performance in this regard. The direct purpose of extracting dirty nitrogen gas is not to cool the water fed into the water cooling tower; rather, dirty nitrogen gas is an unwanted by-product that always accompanies the distillation process. It is possible to utilize the unsaturation of dirty nitrogen gas to cool the water, and I believe this has something to do with latent heat: lol

Thank you all! I have discussed this with the manufacturer, and it is possible to produce as much nitrogen and oxygen as possible.